Commit 67d25186 authored by Harshad Shirwadkar's avatar Harshad Shirwadkar Committed by Theodore Ts'o
Browse files

ext4: drop s_mb_bal_lock and convert protected fields to atomic 



s_mb_buddies_generated gets used later in this patch series to
determine if the cr 0 and cr 1 optimziations should be performed or
not. Currently, s_mb_buddies_generated is protected under a
spin_lock. In the allocation path, it is better if we don't depend on
the lock and instead read the value atomically. In order to do that,
we drop s_bal_lock altogether and we convert the only two protected
fields by it s_mb_buddies_generated and s_mb_generation_time to atomic
type.

Signed-off-by: default avatarHarshad Shirwadkar <harshadshirwadkar@gmail.com>
Reviewed-by: default avatarAndreas Dilger <adilger@dilger.ca>
Reviewed-by: default avatarRitesh Harjani <ritesh.list@gmail.com>
Link: https://lore.kernel.org/r/20210401172129.189766-2-harshadshirwadkar@gmail.com


Signed-off-by: default avatarTheodore Ts'o <tytso@mit.edu>
parent a149d2a5

fs/ext4/ext4.h

+2 −3
Original line number Diff line number Diff line
@@ -1553,9 +1553,8 @@ struct ext4_sb_info { 
	atomic_t s_bal_goals;	/* goal hits */

	atomic_t s_bal_breaks;	/* too long searches */

	atomic_t s_bal_2orders;	/* 2^order hits */

	spinlock_t s_bal_lock;

	unsigned long s_mb_buddies_generated;

	unsigned long long s_mb_generation_time;

	atomic_t s_mb_buddies_generated;	/* number of buddies generated */

	atomic64_t s_mb_generation_time;

	atomic_t s_mb_lost_chunks;

	atomic_t s_mb_preallocated;

	atomic_t s_mb_discarded;

fs/ext4/mballoc.c

+5 −8
Original line number Diff line number Diff line
@@ -816,10 +816,8 @@ void ext4_mb_generate_buddy(struct super_block *sb, 
	clear_bit(EXT4_GROUP_INFO_NEED_INIT_BIT, &(grp->bb_state));



	period = get_cycles() - period;

	spin_lock(&sbi->s_bal_lock);

	sbi->s_mb_buddies_generated++;

	sbi->s_mb_generation_time += period;

	spin_unlock(&sbi->s_bal_lock);

	atomic_inc(&sbi->s_mb_buddies_generated);

	atomic64_add(period, &sbi->s_mb_generation_time);

}



/* The buddy information is attached the buddy cache inode
@@ -2850,7 +2848,6 @@ int ext4_mb_init(struct super_block *sb) 
	} while (i <= sb->s_blocksize_bits + 1);



	spin_lock_init(&sbi->s_md_lock);

	spin_lock_init(&sbi->s_bal_lock);

	sbi->s_mb_free_pending = 0;

	INIT_LIST_HEAD(&sbi->s_freed_data_list);
@@ -2986,9 +2983,9 @@ int ext4_mb_release(struct super_block *sb) 
				atomic_read(&sbi->s_bal_breaks),

				atomic_read(&sbi->s_mb_lost_chunks));

		ext4_msg(sb, KERN_INFO,

		       "mballoc: %lu generated and it took %Lu",

				sbi->s_mb_buddies_generated,

				sbi->s_mb_generation_time);

		       "mballoc: %u generated and it took %llu",

				atomic_read(&sbi->s_mb_buddies_generated),

				atomic64_read(&sbi->s_mb_generation_time));

		ext4_msg(sb, KERN_INFO,

		       "mballoc: %u preallocated, %u discarded",

				atomic_read(&sbi->s_mb_preallocated),